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manual: Add preadv and pwritev documentation

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* manual/llio.texi: Add preadv and pwritev documentation.
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Adhemerval Zanella 2017-05-01 16:38:56 -03:00
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@ -1,3 +1,7 @@
2017-05-04 Adhemerval Zanella <adhemerval.zanella@linaro.org>
* manual/llio.texi: Add preadv and pwritev documentation.
2017-05-04 Joseph Myers <joseph@codesourcery.com>
[BZ #21455]

102
manual/llio.texi
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@ -620,6 +620,10 @@ is not written to the current position of the file descriptor
position @var{offset}. The position of the file descriptor itself is
not affected by the operation. The value is the same as before the call.
However, on Linux, if a file is opened with @code{O_APPEND}, @code{pwrite}
appends data to the end of the file, regardless of the value of
@code{offset}.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{pwrite} function is in fact @code{pwrite64} and the type
@code{off_t} has 64 bits, which makes it possible to handle files up to
@ -662,6 +666,104 @@ When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a
@code{pwrite} and so transparently replaces the 32 bit interface.
@end deftypefun
@comment sys/uio.h
@comment BSD
@deftypefun ssize_t preadv (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is a syscall for Linux 3.2 for all architectures but microblaze
@c (which was added on 3.15). The sysdeps/posix fallback emulation
@c is also MT-Safe since it calls pread, and it is now a syscall on all
@c targets.
This function is similar to the @code{readv} function, with the difference
it adds an extra @var{offset} parameter of type @code{off_t} similar to
@code{pread}. The data is written to the file starting at position
@var{offset}. The position of the file descriptor itself is not affected
by the operation. The value is the same as before the call.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{preadv} function is in fact @code{preadv64} and the type
@code{off_t} has 64 bits, which makes it possible to handle files up to
@twoexp{63} bytes in length.
The return value is a count of bytes (@emph{not} buffers) read, @math{0}
indicating end-of-file, or @math{-1} indicating an error. The possible
errors are the same as in @code{readv} and @code{pread}.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun ssize_t preadv64 (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off64_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is a syscall for Linux 3.2 for all architectures but microblaze
@c (which was added on 3.15). The sysdeps/posix fallback emulation
@c is also MT-Safe since it calls pread64, and it is now a syscall on all
@c targets.
This function is similar to the @code{preadv} function with the difference
is that the @var{offset} parameter is of type @code{off64_t} instead of
@code{off_t}. It makes it possible on 32 bit machines to address
files larger than @twoexp{31} bytes and up to @twoexp{63} bytes. The
file descriptor @code{filedes} must be opened using @code{open64} since
otherwise the large offsets possible with @code{off64_t} will lead to
errors with a descriptor in small file mode.
When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is actually available under the name
@code{preadv} and so transparently replaces the 32 bit interface.
@end deftypefun
@comment sys/uio.h
@comment BSD
@deftypefun ssize_t pwritev (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is a syscall for Linux 3.2 for all architectures but microblaze
@c (which was added on 3.15). The sysdeps/posix fallback emulation
@c is also MT-Safe since it calls pwrite, and it is now a syscall on all
@c targets.
This function is similar to the @code{writev} function, with the difference
it adds an extra @var{offset} parameter of type @code{off_t} similar to
@code{pwrite}. The data is written to the file starting at position
@var{offset}. The position of the file descriptor itself is not affected
by the operation. The value is the same as before the call.
However, on Linux, if a file is opened with @code{O_APPEND}, @code{pwrite}
appends data to the end of the file, regardless of the value of
@code{offset}.
When the source file is compiled with @code{_FILE_OFFSET_BITS == 64} the
@code{pwritev} function is in fact @code{pwritev64} and the type
@code{off_t} has 64 bits, which makes it possible to handle files up to
@twoexp{63} bytes in length.
The return value is a count of bytes (@emph{not} buffers) written, @math{0}
indicating end-of-file, or @math{-1} indicating an error. The possible
errors are the same as in @code{writev} and @code{pwrite}.
@end deftypefun
@comment unistd.h
@comment BSD
@deftypefun ssize_t pwritev64 (int @var{fd}, const struct iovec *@var{iov}, int @var{iovcnt}, off64_t @var{offset})
@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}}
@c This is a syscall for Linux 3.2 for all architectures but microblaze
@c (which was added on 3.15). The sysdeps/posix fallback emulation
@c is also MT-Safe since it calls pwrite64, and it is now a syscall on all
@c targets.
This function is similar to the @code{pwritev} function with the difference
is that the @var{offset} parameter is of type @code{off64_t} instead of
@code{off_t}. It makes it possible on 32 bit machines to address
files larger than @twoexp{31} bytes and up to @twoexp{63} bytes. The
file descriptor @code{filedes} must be opened using @code{open64} since
otherwise the large offsets possible with @code{off64_t} will lead to
errors with a descriptor in small file mode.
When the source file is compiled using @code{_FILE_OFFSET_BITS == 64} on a
32 bit machine this function is actually available under the name
@code{pwritev} and so transparently replaces the 32 bit interface.
@end deftypefun
@node File Position Primitive
@section Setting the File Position of a Descriptor